Narrative:

I was captain on flight from stl to dfw. We were executing the blue ridge 2 STAR arrival to dfw. The first officer was flying that leg in instrument conditions. The aircraft was a 2-M, 2 engine turbo jet. Descending through approximately 26000' I told the first officer I was off ATC to talk to maintenance. We were approximately 110 NM out. This is a normal company procedure where we alert our company maintenance of discrepancies the aircraft has on arrival. While I was off ATC, the first officer received a des clearance which he read back twice. When I heard him repeating the clearance, I returned to monitor ATC and said, 'I'm back.' he said we were clrd to 11000', cross 5 south of blue ridge at 13000' or below, and maintain 11000', cross alkid at 11000'. He set and armed 11000' in the flight director's altitude window. I did not hear the controller's instructions or the first officer's readback (to understand it). We were 6 DME north of blue ridge VOR when going through 13000'. I for some reason called center and reported leaving 13000' for 11000'. The controller immediately came back and said, 'negative, return to 13000' immediately, traffic is ahead at 12000', 4 mi.' I took the aircraft off autoplt and immediately pulled up to 13000'. I saw my altimeter bottom out at 12400'. Just as we arrived back at 13000' the controller said, 'the aircraft is ahead (at 12000') 2 NM's.' I misspoke and said we're at 12000', when I meant 13000' which I corrected. I told the controller that we had understood the clearance as stated above and he said we were clrd to cross 5 south of blue ridge at 13000', then des to cross alkid at 11000'. I acknowledged and we continued the approach uneventfully. The first officer read back the initial clearance twice, then relayed it to me. If he read it back correctly to ATC, he still misunderstood because his version is different than the ATC controller's version. There are several possible contributing factors. The first officer is new (approximately 50 flight hours) to the medium large transport. Although he is an experienced first officer in the large transport, these aircraft have radically different flight directors. Perhaps I should have stayed with him more closely, however this was our sixth leg in 2 days, and he was having no difficulty up to then. My calling company maintenance is a standard procedure which leaves one pilot monitoring ATC when about 100 mi or so out, and is a potential contributing factor to such errors. I intend to make my opinion of this and this incident known to my company. The flight director has the ability to set (arm) one altitude at a time. While the clearance was not unusual if given in either version, I believe it is better not to issue multiple altitude clrncs if possible because of the potential for error. I don't mean to excuse the practice of not writing clrncs down, it's not usually done because of the arming altitude feature, and would not have helped here as the clearance was never properly understood.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION EXCURSION FROM CLRNC ALT DUE CLRNC INTERP.

Narrative: I WAS CAPT ON FLT FROM STL TO DFW. WE WERE EXECUTING THE BLUE RIDGE 2 STAR ARR TO DFW. THE F/O WAS FLYING THAT LEG IN INSTRUMENT CONDITIONS. THE ACFT WAS A 2-M, 2 ENG TURBO JET. DSNDING THROUGH APPROX 26000' I TOLD THE F/O I WAS OFF ATC TO TALK TO MAINT. WE WERE APPROX 110 NM OUT. THIS IS A NORMAL COMPANY PROC WHERE WE ALERT OUR COMPANY MAINT OF DISCREPANCIES THE ACFT HAS ON ARR. WHILE I WAS OFF ATC, THE F/O RECEIVED A DES CLRNC WHICH HE READ BACK TWICE. WHEN I HEARD HIM REPEATING THE CLRNC, I RETURNED TO MONITOR ATC AND SAID, 'I'M BACK.' HE SAID WE WERE CLRD TO 11000', CROSS 5 S OF BLUE RIDGE AT 13000' OR BELOW, AND MAINTAIN 11000', CROSS ALKID AT 11000'. HE SET AND ARMED 11000' IN THE FLT DIRECTOR'S ALT WINDOW. I DID NOT HEAR THE CTLR'S INSTRUCTIONS OR THE F/O'S READBACK (TO UNDERSTAND IT). WE WERE 6 DME N OF BLUE RIDGE VOR WHEN GOING THROUGH 13000'. I FOR SOME REASON CALLED CENTER AND RPTED LEAVING 13000' FOR 11000'. THE CTLR IMMEDIATELY CAME BACK AND SAID, 'NEGATIVE, RETURN TO 13000' IMMEDIATELY, TFC IS AHEAD AT 12000', 4 MI.' I TOOK THE ACFT OFF AUTOPLT AND IMMEDIATELY PULLED UP TO 13000'. I SAW MY ALTIMETER BOTTOM OUT AT 12400'. JUST AS WE ARRIVED BACK AT 13000' THE CTLR SAID, 'THE ACFT IS AHEAD (AT 12000') 2 NM'S.' I MISSPOKE AND SAID WE'RE AT 12000', WHEN I MEANT 13000' WHICH I CORRECTED. I TOLD THE CTLR THAT WE HAD UNDERSTOOD THE CLRNC AS STATED ABOVE AND HE SAID WE WERE CLRD TO CROSS 5 S OF BLUE RIDGE AT 13000', THEN DES TO CROSS ALKID AT 11000'. I ACKNOWLEDGED AND WE CONTINUED THE APCH UNEVENTFULLY. THE F/O READ BACK THE INITIAL CLRNC TWICE, THEN RELAYED IT TO ME. IF HE READ IT BACK CORRECTLY TO ATC, HE STILL MISUNDERSTOOD BECAUSE HIS VERSION IS DIFFERENT THAN THE ATC CTLR'S VERSION. THERE ARE SEVERAL POSSIBLE CONTRIBUTING FACTORS. THE F/O IS NEW (APPROX 50 FLT HRS) TO THE MLG. ALTHOUGH HE IS AN EXPERIENCED F/O IN THE LGT, THESE ACFT HAVE RADICALLY DIFFERENT FLT DIRECTORS. PERHAPS I SHOULD HAVE STAYED WITH HIM MORE CLOSELY, HOWEVER THIS WAS OUR SIXTH LEG IN 2 DAYS, AND HE WAS HAVING NO DIFFICULTY UP TO THEN. MY CALLING COMPANY MAINT IS A STANDARD PROC WHICH LEAVES ONE PLT MONITORING ATC WHEN ABOUT 100 MI OR SO OUT, AND IS A POTENTIAL CONTRIBUTING FACTOR TO SUCH ERRORS. I INTEND TO MAKE MY OPINION OF THIS AND THIS INCIDENT KNOWN TO MY COMPANY. THE FLT DIRECTOR HAS THE ABILITY TO SET (ARM) ONE ALT AT A TIME. WHILE THE CLRNC WAS NOT UNUSUAL IF GIVEN IN EITHER VERSION, I BELIEVE IT IS BETTER NOT TO ISSUE MULTIPLE ALT CLRNCS IF POSSIBLE BECAUSE OF THE POTENTIAL FOR ERROR. I DON'T MEAN TO EXCUSE THE PRACTICE OF NOT WRITING CLRNCS DOWN, IT'S NOT USUALLY DONE BECAUSE OF THE ARMING ALT FEATURE, AND WOULD NOT HAVE HELPED HERE AS THE CLRNC WAS NEVER PROPERLY UNDERSTOOD.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.